Question on ranking .com Vs .co.uk

I have a site that I am targeting a local area in the UK. What's weird is that it ranks #1 in google.com but page 2 in .co.uk. Can anyone shed light on why this would be? I think it could be one of two things:

1. Domain extension is not .co.uk (although site is hosted in UK)
2. Backlinks are not from UK sites

Not sure which one is really causing the problem. I assume it's point 2 but any clarity on this would be greatly appreciated.